Fuel Pump(s)

Difficulty:  Medium
Warning:  Fuel is a hazardous chemical, take appropriate precautions
Recommended Tools:  Wrenches including adjustable, utility knife

The 1980 Porsche 924 Turbo has two fuel pumps in the stock configuration, one in the tank and another external or in-line pump mounted just next to the tank.  Both of these pumps were seized on mine and the replacements are fairly costly so I decided to replace them both with one external pump.

Fuel Pumps

Porsche must have had a reason for using two pumps but there are many applications that put out a good deal more power and run fine with a single pump.  After doing some research I figured that I should be able to use something like a Bosch 044 or Walbro 255 that are reportedly able to supply fuel for 450HP applications.  I wanted an external pump for a simple installation but when I got my hands on the pump I bought, I was surprised at how small the OD is, it looked like it might be close to the stock, in-tank pump.  Sure enough I found an example on a Porsche forum of a guy installing a Walbro 255 in-tank version in place of the stock pump, eliminating the external pump.  As long as you can get a filter on the inlet and the inlet isn’t compromised too much by the tank sidewall, I think that would be a neater solution.  At the time of writing, the in-tank application had not been tested.
This install uses the Walbro GSL392 Installation Kit, a few feet of 3/8 rubber or 8mm nylon high pressure fuel tube, a few feet of 3/8 fuel tube, some suitable hose clamps, a 3/8 inline fuel filter and some small pieces of metal to make right angle mount brackets with suitable nuts and bolts.

One area of concern was whether the pump would have a consistent flow of fuel to the inlet.  I wanted to install a filter between the tank and the pump and hoped that it would not have enough pressure drop to cause cavitation at the pump so to be on the safe side I decided to mount the pump a bit lower to minimize the risk and make best use of the pressure head.

After draining all the fuel and removing the stock pumps, I needed to access the fuel line that goes from the outlet of the external pump, up to the inlet of the accumulator sitting up over the passenger side rear axle.  This hose is an 8mm nylon tube with a rubber sheath and has to be cut to access the Porsche fitting.  My accumulator was a bit rusty and needed to come off for painting, that was when it became apparent that the rubber mounts that hold the accumulator were perished; I found some on Amazon.ca for under $5 by searching “6mm Male Thread 25mmx21mm Rubber Base Vibration Isolator Mount”.  When I removed the accumulator I was fortunate that the fuel outlet hose came off without too much fuss, but the inlet hose nut was jammed to the elbow fitting so I had to spin the whole hose assembly to undo it – much easier with the accumulator out of the car!  Unfortunately my elbow fitting got broken while trying to free up the nut so I used the fitting from the other end of the hose, as shown on the left below with the fuel pump barb fitting on the right.

Fuel pump fittings.jpgThe Porsche fitting (left) is for a plastic hose but the barbs are not very sharp so I was comfortable using flexible high pressure hose and clamps for fuel injection applications.  Since I couldn’t use the elbow, it’s a good job that there is a nice bit of clearance above the accumulator that allows the flex hose to bend smoothly without kinking.  Have to get a picture of the accumulator.

Once made up, the end with the Porsche fitting goes back on the top of the accumulator and then a couple of feet of flex hose is required to reach the fuel pump.  I mounted the fuel pump on the lower two stock brackets using two right angle brackets and four little nuts, bolts and washers.

Fuel Pump Mount 1  Fuel Pump Mount 2

I wanted to run a filter before the inlet of the pump.  Ideally I would have got one that fitted inside the tank on the back of the fuel tank plug, but the only one like that I could find was an original Porsche part so I decided to try a regular inline filter.  No clamps needed on the low pressure side, and regular fuel flexible hose connects the fuel pump inlet to the fuel filter, and then the fuel filter inlet to the tank plug.

Fuel Pump Mount 3

The new pump has been tested with some short drives and is working fine so far, but on the last drive I noticed that I could hear it whining quite clearly in the back.  I understand that the Walbro pump uses metal gears that makes them relatively noisy so the in-tank solution is probably much quieter.  With my external mount, if it does get too annoying, I could swap out the pump for one with plastic gears.